A water pump used for circulating coolant water for an automobile engine is disclosed for example in Japanese Patent Publication No. Tokukai Hei 8-254213, and is constructed as shown in FIG. 10. A cylindrical housing 1 has a mounting flange 2 formed around its outer peripheral surface on the inside end (the inside with reference to the axial direction is the side nearest the engine, and is the right side in all of the figures) which is used for fastening to the cylinder block of the engine. A rolling bearing unit 6 comprising a ball bearing 4 on the inside and a roller bearing 5 on the outside (the outside with reference to the axial direction is the side furthest from the engine, and is the left side in all of the figures) in combination to rotatably support a rotating shaft 3, is provided on the inner diameter side of the housing 1. Seal rings 7, 7 are located on both ends in the axial direction (left and right direction in FIG. 10) of this rolling bearing unit 6 to prevent leakage of grease filled inside the bearing unit, as well as to prevent entry of foreign matter such as dirt or steam from the outside. Moreover, a pulley 8 is fastened to a section on the outside end of the aforementioned rotating shaft 3 protruding from the opening on the outside end of the housing 1.
When installed in the engine, a belt (not shown in the figure) is placed around this pulley 8 to rotate and drive the aforementioned rotating shaft 3 through the crankshaft of the engine. On the other hand, an impeller 9 is fastened to a section on the inside end of the rotating shaft 3 protruding from the inside surface of the mounting flange 2. When this mounting flange 2 is fastened to the cylinder block of the engine, the aforementioned impeller 9 fits inside the water jacket formed within the cylinder block. With rotation of the rotating shaft 3, the cooling water in the water jacket circulates to and from a radiator (not shown in the figure) or the like.
Furthermore, a mechanical seal 10 is provided between the outer peripheral surface of the rotating shaft 3 and the inner peripheral surface of the housing 1. When the engine is operating, this mechanical seal 10 allows rotation of the rotating shaft 3 while preventing leakage of steam or coolant water flowing inside the water jacket, to the outside. However, it is difficult to obtain a perfect seal with the aforementioned mechanical seal 10, and generation of frictional heat at the seal surface of this mechanical seal 10 results in evaporation of the coolant water containing chemical matter such as anti-freeze agents or anti-rust agents, forming steam, and leakage toward the rolling bearing unit 6, while at the same time, the coolant water wherein the aforementioned chemical matter is condensed due to evaporation also leaks out to the rolling bearing unit 6 side. Therefore a slinger 11 is located in the middle section of the rotating shaft 3 between the mechanical seal 10 and the inside seal ring 7, and a supply-discharge hole (not shown in the figure) is formed in the middle of the housing 1 in the section facing the outer peripheral edge of the slinger 11 to allow unrestricted discharge of steam or hot water leaking from the mechanical seal 10, to the outside of the housing 1. In other words, the aforementioned supply-discharge port communicates between the outside and a space which is provided between the mechanical seal 10 and the inside seal ring 7 in the axial direction to function as a steam chamber, so that steam and hot water in this space are discharged freely to the outside.
In the first example of the conventional construction shown in FIG. 10, the inner peripheral edges of a pair of seal lips 12, 12 forming the inside seal ring 7 come into sliding contact around the entire periphery of the outer peripheral surface of the middle section of the rotating shaft 3. Moreover, the inside seal ring 7 and the slinger 11 are not associated with, and are independent of, each other.
On the other hand, Japanese Patent Publication No. Tokukai Hei 11-153096 discloses, as shown in FIG. 11, a construction for improving seal performance by locating a seal ring 7a and a slinger 11a such that they are associated with each other. In the case of this construction, two of three lips 12a, 12b and 12c constituting the seal ring 7a, specifically the seal lips 12a and 12b, come into sliding contact around the entire periphery of the outer peripheral surface of the rotating shaft 3a. On the other hand, the tip edge of the remaining seal lip 12c comes into sliding contact around the entire periphery of the outside surface of the slinger 11a. With this kind of construction, the seal performance is improved in comparison to that of the first example of the conventional construction shown in FIG. 10, and it is possible to more effectively prevent foreign matter such as steam or hot water from entering the rolling bearing unit supporting the rotating shaft 3a. 
In the case of the second example of the construction shown in FIG. 11, the seal performance is better than that of the first example of the construction shown in FIG. 10. However in order to effectively prevent foreign matter from entering the bearing unit over a long period of time, further improvement is desired. In other words, in Japanese Patent Publication No. Tokukai Hei 11-153096 wherein the construction as shown in FIG. 11 is disclosed, only a construction wherein the tip edge of one of the three seal lips 12a, 12b, and 12c forming the seal lip 7a, specifically the seal lip 12c, is in sliding contact with the outside surface of the slinger 11 is disclosed, but no detailed specifications are disclosed.
On the other hand, in order to effectively prevent entry of foreign matter into the bearing unit over a long period of time, it is necessary to satisfy the following conditions (1) and (2).    (1) The tip edge of the seal lip 12c must come into sliding contact around the entire periphery of the outside surface of the slinger 11a without gaps and with sufficient pressure.    (2) Wear of the tip edge of the seal lip 12c due to rubbing with the outside surface of the slinger 11a must be minimized.
If only condition (1) above is to be satisfied, it is only necessary to increase the amount of elastic deformation of the seal lip 12c and increase the force pressing the tip edge of the seal lip 12c against the outside surface of the slinger 11a. On the other hand, if only condition (2) above is to be satisfied, it is only necessary to reduce the amount of elastic deformation of the seal lip 12c and reduce the force pushing the tip edge of the seal lip 12c against the outside surface of the slinger 11a. 
Since the condition (1) above for securing the seal performance is counter to the condition (2) above for securing durability, it is important to implement a specific construction to effectively prevent entry of foreign matter over a long period of time, and to obtain a method of assembly of that construction providing a satisfactory yield with an industrial method.
The methods of assembly for the seal apparatus for a water pump, the rotation support apparatus for a water pump, and the water pump of the present invention has been invented in consideration of the aforementioned situation.